The present invention relates to an apparatus and method for forming paper and a fourdrinier paper machine. More particularly, but not by way of limitation, the present invention relates to a method and apparatus for removing liquid from a web formed on a fourdrinier wire and for subsequently urging the web off of the wire.
Since its first introduction, the fourdrinier paper machine has been the most efficient apparatus for producing paper. The suitability of a modern fourdrinier machine is, however, determined by a variety of factors. The machine should operate at the highest possible speed and yet be compact in size and include the fewest possible number of moving parts. Also, it is important that the machine form a web of fibers oriented in a substantially random array so that the paper produced has the maximum possible strength. Papers having fibers in linear orientation tend to be weaker in one dimension than papers containing randomly oriented fibers.
Unfortunately, these goals tend to be mutually exclusive and have forced the paper machine designer to sacrifice one or more qualities when constructing the fourdrinier machine. Typically, the length of a machine's forming table must be increased if the machine is to operate at a high speed. This is because a high speed machine more rapidly moves the web past suction boxes and other dewatering devices. Each individual such device has less time to act on the web so the forming table must be extended in order to accomodate a greater number of such devices.
Increasing wire speed also has a detrimental effect on paper bursting strength and drying steam requirement since the percentage of fibers oriented parallel to the web increases. Such a layered web delaminates and bursts at a relatively low pressure and is insufficiently porous to facilitate rapid steam drying.
The various existing apparatuses designed for producing fiber disorientation, such as the deflector bars shown in U.S. Pat. No. 3,489,644 (Rhine), further increase the length of the fourdrinier paper machine. Similarly, U.S. Pat. No. 1,536,599 (Aldrige), No. 2,092,798 (Charlton) and No. 2,095,378 (Charlton) show devices for shaking a fourdrinier wire to disorient fibers. Such devices substantially increase the required length of the wire and do not assist in removing liquid from the web.
Recently, the speed and quality of paper formation have been enhanced by forming the web between two superposed wires of a twin-wire fourdrinier machine as is described in greater detail below. Because such twin-wire machines are very fast and do not in and of themselves solve the problem of liquid removal, they must be very long to contain a suitable number of dewatering devices. Furthermore, webs formed on such a machine are deeply settled in the wires and are thus difficult to transfer off of the wires of the forming section.